AP Chemistry : Periodic Trends

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

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Example Question #1 : Periodic Trends

Which of the following elements is the most electronegative?

Possible Answers:

Gallium

Titanium

Phosphorous

Barium

Helium

Correct answer:

Phosphorous

Explanation:

Electronegativity increases across a period (going right) and decreases down a group [not including noble gases]. The element closest to the top right is Phosphorous

Example Question #1 : Periodic Trends

Which of the following can contain atoms that can have multiple oxidation states?

Possible Answers:

Alkaline earth metals

Halogens

Transition metals

Alkali metals

Correct answer:

Transition metals

Explanation:

The transition metals are capable of losing various numbers of electrons from the s and d orbitals of the valence shell. Metals such as Cu, Fe, and Mn have various oxidation states and can form many different ionic compounds.

Example Question #1 : Periodic Trends

Which of the following has the highest electron affinity?

Possible Answers:

Correct answer:

Explanation:

The trend for electron affinity increases upwards through a group, and rightwards along a period. The noble gasses already have full octets, so the increasing trend stops at the halogens and the noble gasses have extremely low values. The element with the highest electron affinity is fluorine. Halogens tend to have a high values so that they can complete their almost full valence shells. Bromine has a very high electron affinity, while the bromide ion does not because it has already filled its valence octet.

Example Question #4 : Periodic Trends

Which of the following has the highest electronegativity value?

Possible Answers:
Mercury
Zinc
Flourine
Cesium
Correct answer: Flourine
Explanation:

Electronegativity increases as one moves across a period (row) from left to right, or up a group (column) from bottom to top. Following these trends, fluorine is the most electronegative element.

Example Question #2 : Periodic Trends

Which of the following has the highest electronegativity: Cl, Ba, Mg, S?

Possible Answers:

Cl

Ba

S

Mg

Correct answer:

Cl

Explanation:

Electronegativity measures the ability an atom to attract shared electrons
in bond. It follows a trend that it increases moving from left to right and down to up across
the periodic table.

Example Question #2 : Periodic Trends

Which group of elements can be predicted to have the lowest second ionization energy?

Possible Answers:

Group VII

Group V

Group VIII

Group II

Group I

Correct answer:

Group II

Explanation:

Ionization energy is the energy required to completely remove an electron from an atom.  The electron that would be removed is the atoms most loosely held electron.  Some atoms are more likely to give up an electron to get to a more stable electron configuration.  This is the reason that Group I elements have the lowest first ionization energy because after loosing one electron, these elements have now acheived an octet configuration. The second ionization energy is the energy to remove a second electron from an atom.  This will be lowest for the Group II elements because these elements acheive an octet configuration after loosing two electrons.  

Example Question #6 : Periodic Trends

Which of the following elements has the largest atomic radius?

Possible Answers:

Cs

F

I

Na

Sr

Correct answer:

Cs

Explanation:

Atomic radius increases down the columns and to the left. The furthest left elements are Na and Cs. Cs is furthest down so it is the biggest.

Example Question #4 : Periodic Trends

Which of the following has the LARGEST atomic radius

Possible Answers:

Fr

F

Na

H

Rn

Correct answer:

Fr

Explanation:

Atomic radius expands down the columns and to the LEFT.

Example Question #2 : Periodic Trends

Which of the following has the smallest atomic radius?

Possible Answers:
Li
Na
Rb
K
Cs
Correct answer: Li
Explanation:

Atomic radius INCREASES DOWN and TO THE LEFT in the periodic table

Example Question #2 : Periodic Trends

When considering trends in the periodic table of elements.  How do the atomic radii of elements in a the same period change as one moves from left to right?

Possible Answers:
Increasing then Decreasing
Increasing
Decreasing
There is no discernible trend, it is completely random
Decreasing then Increasing
Correct answer: Decreasing
Explanation:

If we look at elements of the same period the prinicipal quantum number for each one of these elements is the same.  Thus the outermost energy level for the electrons of each atom is the same.  If we consider moving through the periodic table in numerical order, the left side of the periodic table features atoms  that have just begun to add electrons to new energy levels.  On the right side of the periodic table the elements are moving closer to filling the energy level.  The differences in atomic radii are the result of differing amounts of protons between atoms whose electrons are in the same energy level.  K has one electron in the fouth energy level and Kr has eight electrons in the fouth energy level.  K has 19 protons with which to generate pull on the electrons.  Kr has 36  protons with which to generate pull on the electrons.  Thus Kr has a smaller atomic radius becasue of its ability to have a tighter grasp on its electrons becasue of the stronger charge generated by its nucleus.  

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